Thermoplastic polyurethane and use thereof

ABSTRACT

Thermoplastic polyurethanes comprise segments A formed of a high molecular weight diol, segments B formed of at least one low molecular weight diol selected from 1,4-bis(hydroxyethoxy)benzene and 1,3-propanediol, and segments C formed of a polyisocyanate. These segments A, B and C are bonded together in a linear form by urethane bonds. The segments B account for 1 to 30 wt. % in the thermoplastic polyurethane. These thermoplastic polyurethanes are characterized in that they have high impact resilience and also in that their impact resilience does not drop much in a low temperature range, in other words, their impact resilience does not vary much depending on changes in outdoor temperature.

TECHNICAL FIELD

This invention relates to thermoplastic polyurethanes (hereinaftersimply called “polyurethanes”), which have high impact resilience, donot vary much in impact resilience depending on changes in temperatureand are useful especially as cover materials for golf balls, and also tomolding compositions making use of the polyurethanes.

BACKGROUND ART

Polyurethanes have high strength and are excellent in properties such asabrasion resistance and flexing resistance, and have been used for manyyears in applications such as pressure hoses, packings, conveyor beltsand soles. In the field of golf balls, on the other hand, polyurethaneshave been finding utility as cover materials for multi-piece golf balls(may hereinafter be called simply “golf balls”) in recent years fortheir spin characteristics, flight performance, hit feel (a feel uponhitting a golf ball), durability, mass productivity, and the like (seeJP-A-6-182002, JP-A-9-271538, JP-A-11-178949 and JP-A-11-253580). Thepolyurethanes used as cover materials in such conventional golf ballsare, however, accompanied by drawbacks that their impact resilience isnot very high and varies significantly with temperature and that theirimpact resilience drops considerably especially when the outdoortemperature is low. There is, accordingly, an outstanding desire for thesolution of these problems.

Therefore, an object of the present invention is to provide apolyurethane improved in the above-described drawbacks of theconventional polyurethanes, especially a polyurethane useful as a covermaterial for golf balls.

DISCLOSURE OF THE INVENTION

To achieve the above-described object, the present inventors haveproceed with a variety of investigations. As a result, it has been foundthat a polyurethane making use of 1,4-bis(hydroxyethoxy)benzene(hereinafter called “BHEB”) and/or 1,3-propanediol as a low molecularweight diol in combination with a high molecular weight diol uponproduction of the polyurethane is characterized in that it has highimpact resilience and also in that its impact resilience does not dropmuch in a low temperature range, in other words, its impact resiliencedoes not vary much depending on changes in outdoor temperature. Thosefindings have then led to the completion of the present invention.

The above-described object can be achieved by the present invention tobe described hereinafter. Specifically, the present invention provides apolyurethane comprising segments A formed of a high molecular weightdiol, segments B formed of at least one low molecular weight diolselected from BHEB and 1,3-propanediol, and segments C formed of apolyisocyanate. The segments A, B and C are bonded together in a linearform by urethane bonds. The segments B account for 1 to 30 wt. % in thepolyurethane.

In the above-described present invention, it is preferred that thepolyurethane further comprises segments D formed of a low molecularweight diol other than BHEB or 1,3-propanediol; or that the segments Aeach comprises a segment E formed of a polysiloxane diol or modifiedpolysiloxane diol.

In the above-described present invention, the high molecular weight diolcan be at least one diol having a number average molecular weight offrom 600 to 4,000 and selected from the group consisting ofpolytetramethylene ether glycol (hereinafter called “PTMG”),polybutylene adipate diol, polycarbonate diols and polysiloxane diols,the low molecular weight diol can be BHEB, the polyisocyanate can be4,4′-diphenylmethanediisocyanate (hereinafter called “MDI”), and thesehigh molecular weight diol, low molecular weight diol and polyisocyanatecan be used in proportions of 100 parts by weight, from 10 to 120 partsby weight and from 20 to 170 parts by weight, respectively. Thispolyurethane is useful for various molded products.

In the above-described present invention, the high molecular weight diolcan be PTMG having a number average molecular weight of from 1,000 to2,000, the low molecular weight diol can be BHEB, the polyisocyanate canbe MDI, and these high molecular weight diol, low molecular weight dioland polyisocyanate can be used in proportions of 100 parts by weight,from 11 to 42 parts by weight and from 39 to 76 parts by weight,respectively. This polyurethane is useful for various molded productsincluding a cover material for golf balls.

In the above-described present invention, the high molecular weight diolcan be PTMG having a number average molecular weight of from 800 to1,200, the low molecular weight diol can be BHEB, the polyisocyanate canbe MDI, and these high molecular weight diol, low molecular weight dioland polyisocyanate can be used in proportions of 100 parts by weight,from 20 to 30 parts by weight and from 50 to 60 parts by weight,respectively. This polyurethane is useful especially as a cover materialfor golf balls.

The polyurethane according to the present invention is suited as a covermaterial for golf balls especially when its impact resilience at 23° C.is from 50 to 90% or when its impact resilience at 0° C. is as much asat least 0.6 times of its impact resilience at 23° C.

The present invention also provides a molding composition comprising asa polymer component the polyurethane according to present invention. Theabove-described polyurethanes and molding composition according to thepresent invention are usable as various molding resins and are usefulespecially as cover materials for gold balls.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will next be described in further detail based onbest modes for preferably carrying out the invention. While thepolyurethane according to the present invention is useful for variousapplications, it is useful especially as a cover material for golfballs. Taking cover materials for golf balls as a representative exampleof its applications, the present invention will be describedhereinafter.

The present invention relates to a polyurethane useful as a covermaterial to form a cover of a golf ball which is formed of a core andthe cover, and the polyurethane is characterized in that it has beensynthesized using BHEB and/or 1,3-propanediol as a low molecular weightdiol, that is, a raw material for the synthesis of polyurethane.

Employed as golf balls include two-piece golf balls formed of a core anda single layer of a cover and having a structure that the core made of acrosslinked cis-1,4-polybutadiene or the like excellent in impactresilience is covered with the cover made of a cover material such as apolyurethane; and three-piece golf balls with an additional coverapplied on the two-piece golf ball to have covers in two layers. Thepolyurethane according to the present invention is useful as a covermaterial for forming covers of such golf bolls.

A polyurethane is generally obtained by reacting a high molecular weightdiol and a polyisocyanate with each other. However, the polyurethaneaccording to the present invention is obtained by using BHEB and/or1,3-propane diol and optionally, a further low molecular weight diolsuch as 1,4-butanediol in combination with a high molecular weight dioland then reacting them with a polyisocyanate. Of BHEB and1,3-propanediol, the particularly preferred low molecular weight diol isBHEB.

The above-described polyurethane according to the present invention canbe expressed as one having a repetition of bonding units as represented,for example, by the formula {-(A-C—B—C—B)-}, in which A represents asegment formed of a high molecular weight diol, B represents a segmentformed of BHEB and/or 1,3-propanediol, and C represents a segment formedof a polyisocyanate. These individual segments are bonded together byurethane bonds. In the present invention, the segments B are containedin a proportion of from 1 to 30 wt. % in the polyurethane. It is to benoted that the above-described formula is illustrative and is changeabledepending on the kinds and proportions of raw materials employed uponproduction of the polyurethane.

As the high molecular weight diol which makes up the segments A in thepresent invention, it is possible to use any one of known high molecularweight diols employed to date in the production of polyurethanes,although those having a number average molecular weight of from 1,000 to10,000 (by the end-group analysis) are preferred. Examples of the highmolecular weight diol include polyester diols, polyetherdiols,polycarbonate diols, polylactone diols, and polysiloxane diols.

Polyester diols are available from condensation polymerization, forexample, between dibasic acids (succinic acid, glutaric acid, adipicacid, sebacic acid, fumaric acid, maleic acid, terephthalic acid,isophthalic acid, naphthalenedicarboxylic acid, tartaric acid, oxalicacid, malonic acid, pimelic acid, suberic acid, glutaconic acid, azelaicacid, 1,4-cyclohexanedicarboxylic acid, α-hydromuconic acid,β-hydromuconic acid, α-butyl-α-ethylglutaric acid, α,β-diethylsuccinicacid, and the like) or their anhydrides and glycols (for example,aliphatic glycols such as ethylene glycol, diethylene glycol,triethylene glycol, dipropylene glycol, tripropylene glycol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,3-methyl-1,5-pentanediol, 1,8-octanediol, 1,9-nonanediol and neopentylglycol; alicyclic glycols such as bishydroxymethylcyclohexane andcyclohexane-1,4-diol; aromatic glycols such as xylylene glycol) orC₁-C₁₈ alkylenediethanolamines. Illustrative polyester diols includecondensation polyester diols such as polyethylene adipate diol,polybutylene adipate diol, and polyhexamethylene adipate diol.

Illustrative polylactone diols include lactone polyester diols such aspolylactone diol, polycaprolactone diol and polymethylvalerolactonediol, which can be obtained by subjecting lactone to ring-openingpolymerization while using the above-described diols as initiators.

Illustrative polyether diols include homopolyether diols of alkyleneoxides, such as PTMG, polyethylene ether glycol and polypropylene etherglycol; and copolyether diols of different alkylene oxides.

Illustrative polycarbonate diols include poly-1,6-hexanecarbonate dioland poly-1,4-butylenecarbonate diol.

Use of a polysiloxane diol as a part or the entire part of the highmolecular weight diol is preferred in the present invention. Usableexamples include polysiloxane diols represented by the following formula(I), (II) or (III) although known polysiloxane diols are usable. Thesepolysiloxane diols can each form the segments E in the polyurethaneaccording to the present invention.

wherein R^(1a) to R^(1h) each independently represents an alkyl grouphaving 1 to 8 carbon atoms or an aryl group, R^(2a) to R^(2c) eachindependently represents an alkylene group or a divalent substituentgroup containing an ester bond or ether bond, and n stands for aninteger of from 1 to 300 or so.

Specific examples of such polysiloxane diols include the followingpolysiloxane diols:

In the present invention, BHEB and/or 1,3-propanediol is used as a lowmolecular weight diol in combination with the above-described highmolecular weight diol upon production of the polyurethane. In additionto the low molecular weight diol or diols, a further low molecularweight diol can also be used in combination as needed. The further lowmolecular weight diol forms the segments D in the polyurethane accordingto the present invention.

As the further low molecular weight diol, it is possible to use any oneof known low molecular weight diols which have been used conventionallyin the production of polyurethanes. However, preferred are those havingnumber average molecular weights not greater than 250 as measured by theend-group analysis. Illustrative are aliphatic glycols such as ethyleneglycol, diethylene glycol, triethylene glycol, dipropylene glycol,tripropylene glycol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,3-methyl-1,5-pentanediol, 1,8-octanediol, 1,9-nonanediol and neopentylglycol; alicyclic glycols such as bishydroxymethylcyclohexane andcyclohexane-1,4-diol; and aromatic glycols such as xylylene glycol.

BHEB and/or 1,3-propanediol is used in such a proportion that thesegments B formed of the diol or diols account for 1 to 30 wt. %, morepreferably 5 to 25 wt. % in the resulting polyurethane. An excessivelysmall proportion of these segments B will result in a polyurethane thehardness of which will be too low, while an unduly large proportion ofthem will lead to a polyurethane the impact resilience of which will below. When BHEB and/or 1,3-propanediol is used in combination with afurther low molecular weight diol, the proportion of BHEB and/or1,3-propanediol may account for 30 wt. % or more but less than 100 wt.%, preferably 65 wt. % or more but less than 100 wt. %. A proportion ofBHEB and/or 1,3-propanediol smaller than 30 wt. % or greater than 65 wt.% is not preferred, because a proportion of BHEB and/or 1,3-propanediolsmaller than 30 wt. % will result in a polyurethane with low impactresilience while a proportion of BHEB and/or 1,3-propanediol greaterthan 65 wt. % will lead to a polyurethane with high impact resilience.

No particular limitation is imposed on the polyisocyanate for use in thepresent invention, and known polyisocyanates are all usable.Illustrative are aliphatic isocyanates such as 1,6-hexamethylenediisocyanate (HDI), 2,2,4-trimethylhexamethylene diisocyanate, lysinemethyl ester diisocyanate, methylene diisocyanate, isopropylenediisocyanate, lysinediisocyanate, 1,5-octylenediisocyanate and dimeracid diisocyanates; alicyclic isocyanates such as4,4′-dicyclohexylmethane diisocyanate, isophorone diisocyanate (IPDI),hydrogenated tolylene diisocyanate, methylcyclohexane diisocyanate andisopropylidene dicyclohexyl-4,4′-diisocyanate; and aromatic isocyanatessuch as 2,4- or 2,6-tolylene diisocyanate (TDI), MDI, 1,5-naphthylenediisocyanate, xylylene diisocyanate (XDI), triphenylmethanetriisocyanate, tris(4-phenylisocyanate) thiophosphate, trizinediisocyanate, p-phenylene diisocyanate, diphenyl ether diisocyanate anddiphenylsulfone diisocyanate.

The polyurethane according to the present invention can be obtained byreacting the above-described components. As its production process,known polyurethane production processes can each be used. It ispreferred to use the high molecular weight diol (s) and low molecularweight diol(s) and the polyisocyanate at such a ratio that the NCO/OHequivalent ratio falls within a range of from 0.95 to 1.10.

In the polyurethane according to the present invention, the highmolecular weight diol can be at least one diol having a number averagemolecular weight of from 600 to 4,000 and selected from the groupconsisting of PTMG, polybutylene adipate diol, polycarbonate diols andpolysiloxane diols, the low molecular weight diol can be BHEB, thepolyisocyanate can be MDI, and these high molecular weight diol, lowmolecular weight diol and polyisocyanate can be used in proportions of100 parts by weight, from 10 to 120 parts by weight and from 20 to 170parts by weight, respectively. Such polyurethanes are useful forproducing various molded products.

In the polyurethane according to the present invention, the highmolecular weight diol can be PTMG having a number average molecularweight of from 1,000 to 2,000, the low molecular weight diol can beBHEB, the polyisocyanate can be MDI, and these high molecular weightdiol, low molecular weight diol and polyisocyanate can be used inproportions of 100 parts by weight, from 11 to 42 parts by weight andfrom 39 to 76 parts by weight, respectively. Such polyurethanes areuseful for producing various molded products including cover materialsfor golf balls.

In the polyurethane according to the present invention, the highmolecular weight diol can be PTMG having a number average molecularweight of from 800 to 1,200, the low molecular weight diol can be BHEB,the polyisocyanate can be MDI, and these high molecular weight diol, lowmolecular weight diol and polyisocyanate can be used in proportions of100 parts by weight, from 20 to 30 parts by weight and from 50 to 60parts by weight, respectively. Such polyurethanes are useful especiallyas cover materials for golf balls.

The polyurethane according to the present invention may preferably havean impact resilience at 23° C. of from 50 to 90%. If the impactresilience at 23° C. is lower than 50%, golf balls produced using such apolyurethane as a cover material are poor in travel performance. If theimpact resilience at 23° C. is higher than 90%, on the other hand, thesynthesis of such a polyurethane itself is difficult. Further, thepolyurethane according to the present invention may desirably have aratio of its impact resilience (Rb) at 0° C. to its impact resilience at23° C. (Rb(0° C.)/Rb(23° C.)) of 0.60 or greater. If this ratio issmaller than 0.60, balls produced using such a polyurethane as a covermaterial considerably vary in travel distance and hit feel depending onwhether the outdoor temperature is high or low. In addition, thepolyurethane according to the present invention may preferably have ahardness in a range of from JIS A60 to JIS D80 as measured in accordancewith JIS K7311.

The polyurethane according to the present invention can be usedespecially as a cover material for multi-piece golf balls. It can alsobe used as an intermediate-layer-forming material for multi-piece golfballs which are each formed from a core, an intermediate layer and acover. When the polyurethane according to the present invention is usedas a cover material for golf balls, it can be used in the form of amolding composition which contains the polyurethane according to thepresent invention as a principal component and may also use otherpolymer(s) in combination as needed. Further, conventional additivessuch as colorants, antioxidants, ultraviolet light absorbers and partingagents can also be added to the composition.

Taking the cover material for golf balls as a representative example,the application of the polyurethane according to the present inventionhas been described above. However, the application of the polyurethaneaccording to the present invention is not limited to a cover materialfor golf balls, and the polyurethane according to the present inventionis also useful as materials, for example, for industrial parts orcomponents such as gears, packings, rollers, casters, high-impact tubes,high impact hoses, wire coverings, high-impact belts and high-impactfilms and also for sports goods such as sports shoes and bowling pins.

EXAMPLES

The present invention will hereinafter be described more specificallybased on Examples and Comparative Examples, in which the designations“part” or “parts” and “%” are on a weight basis unless otherwisespecifically indicated.

The strength properties and hardness of the polyurethane in each of theExamples and Comparative Examples were measured following JIS K7311, andits impact resilience was measured following JIS K7311, all on a Lupketesting equipment. Further, its flow properties were measured by a Kokaflow tester equipped with a 1 mm (diameter)×10 mm (length) nozzle underthe conditions of 4.9 MPa (50 kgf/cm²) load and 3° C./min heating rate.

Example 1

In polybutylene adipate diol having a number average molecular weight of2,000 (1,000 parts), BHEB (196 parts) and MDI (387 parts) were evenlymixed with stirring, and the resulting mixture was poured into a tray,followed by a reaction at 110° C. After the thus-obtained reactionproduct was crushed, it was pelletized at 200 to 230° C. through anextruder into pellets of a polyurethane (U1). Those pellets were formedinto specimens by injection molding (in the subsequent Examples andComparative Examples, specimens were formed likewise), and they weremeasured for hardness, strength properties (23° C.), flow properties andimpact resilience (0° C., 23° C.) The measurement results are presentedin Table 1.

Example 2

In PTMG having a number average molecular weight of 1,700 (1,000 parts),BHEB (178 parts) and MDI (401 parts) were evenly mixed with stirring,and the resulting mixture was poured into a tray, followed by a reactionat 110° C. Subsequently, a pelletized polyurethane (U2) was obtained ina similar manner as in Example 1. The results of measurements of variousproperties of that polyurethane are presented in Table 1.

Example 3

In poly-ε-caprolactone diol having a number average molecular weight of2,000 (1,000 parts), BHEB (200 parts) and MDI (393 parts) were evenlymixed with stirring, and the resulting mixture was poured into a tray,followed by a reaction at 110° C. Subsequently, a pelletizedpolyurethane (U3) was obtained in a similar manner as in Example 1. Theresults of measurements of various properties of that polyurethane arepresented in Table 1.

Example 4

In hexamethylene carbonate diol having a number average molecular weightof 2,000 (1,000 parts), BHEB (189 parts) and MDI (378 parts) were evenlymixed with stirring, and the resulting mixture was poured into a tray,followed by a reaction at 110° C. Subsequently, a pelletizedpolyurethane (U4) was obtained in a similar manner as in Example 1. Theresults of measurements of various properties of that polyurethane arepresented in Table 1.

Example 5

In an ester-modified polysiloxane diol having a number average molecularweight of 5,200 and a siloxane content of 60% (1,000 parts) and PTMGhaving a number average molecular weight of 1,700 (450 parts), BHEB (258parts) and MDI (514 parts) were evenly mixed with stirring, and theresulting mixture was poured into a tray, followed by a reaction at 110°C. Subsequently, a pelletized polyurethane (U4) was obtained in asimilar manner as in Example 1. The results of measurements of variousproperties of that polyurethane are presented in Table 1. Theester-modified polysiloxane diol had been obtained beforehand bycopolymerizing an alcohol-modified siloxane oil (“KF-6002”, product ofShin-Etsu Chemical Co., Ltd.), which had a number average molecularweight of 3,200 and the below-described structure, with ε-caprolactone.

-   -   (n: a number required to give an OH value of 35)

Comparative Example 1

In PTMG having a number average molecular weight of 1,700 (1,000 parts),1,4-butanediol (111 parts) and MDI (474 parts) were evenly mixed withstirring, and the resulting mixture was poured into a tray, followed bya reaction at 100° C. Subsequently, a pelletized polyurethane (U6) wasobtained in a similar manner as in Example 1. The results ofmeasurements of various properties of that polyurethane are presented inTable 1.

Comparative Example 2

In polybutylene adipate diol having a number average molecular weight of2,000 (1,000 parts), 1,4-butanediol (153 parts) and MDI (573 parts) wereevenly mixed with stirring, and the resulting mixture was poured into atray, followed by a reaction at 100° C. Subsequently, a pelletizedpolyurethane (U7) was obtained in a similar manner as in Example 1. Theresults of measurements of various properties of that polyurethane arepresented in Table 1. TABLE 1 Impact Impact Flow resilience (%)resilience Hardness M100 TB EB beginning Melt viscosity (1) (2) ratio PU(JIS A) (MPa) (MPa) (%) temp. (° C.) (dPa · s: 210° C.) 0° C. 23° C.((1)/(2)) Ex. 1 U1 88 7.6 37.3 385 188 1.7 × 10⁴ 44.1 61.1 0.72 Ex. 2 U285 7.2 36.7 410 179 1.6 × 10⁴ 55.2 74.6 0.74 Ex. 3 U3 92 8.1 40.2 374212 2.3 × 10⁴ 46.8 62.5 0.75 Ex. 4 U4 91 8.2 36.7 388 204 2.1 × 10⁴ 43.360.9 0.71 Ex. 5 U5 85 7.1 18.7 352 181 4.8 × 10⁴ 63.1 78.9 0.80 Comp.Ex. 1 U6 88 7.6 38.4 506 182 1.8 × 10⁴ 18.3 41.5 0.44 Comp. Ex. 2 U7 927.8 45.5 452 198 4.1 × 10⁴ 14.5 36.5 0.40(Note)PU: polyurethaneM100: 100% modulusTB: Tensile strength at breakEB: Elongation at break

From the results of Table 1, the polyurethanes (U1 to U5) of Examples 1to 5, which contained BHEB within the range of from 1 to 30%, had impactresiliences at 23° C. of from 50 to 90%, and moreover, their impactresiliences at 0° C. were as high as 0.60 times or more of their impactresiliences at 23° C. It is, therefore, understood that they had highimpact resiliences not affected by changes in outdoor temperature andare suited as cover materials for golf balls. In the BHEB-freepolyurethanes (U6, U7) of Comparative Examples 1 and 2, on the otherhand, their impact resiliences at 23° C. were not greater than 50%, andtheir impact resiliences at 0° C. were not greater than 0.60 times oftheir impact resiliences at 23° C. It is, therefore, understood thattheir impact resiliences are affected considerably by changes in outdoortemperature and they are not suited as cover materials for golf balls.

Example 6

In polybutylene adipate diol having a number average molecular weight of2,000 (1,000 parts), 1,3-propanediol (124 parts) and MDI (554 parts)were evenly mixed with stirring, and the resulting mixture was pouredinto a tray, followed by a reaction at 100° C. Subsequently, apelletized polyurethane (U8) was obtained in a similar manner as inExample 1. The results of measurements of various properties of thatpolyurethane are presented in Table 2.

Example 7

In PTMG having a number average molecular weight of 1,700 (1,000 parts),1,3-propanediol (98 parts) and MDI (487 parts) were evenly mixed withstirring, and the resulting mixture was poured into a tray, followed bya reaction at 100° C. Subsequently, a pelletized polyurethane (U9) wasobtained in a similar manner as in Example 1. The results ofmeasurements of various properties of that polyurethane are presented inTable 2.

Example 8

In poly-ε-caprolactone diol having a number average molecular weight of2,000 (1,000 parts), 1,3-propanediol (105 parts) and MDI (490 parts)were evenly mixed with stirring, and the resulting mixture was pouredinto a tray, followed by a reaction at 100° C. Subsequently, apelletized polyurethane (U10) was obtained in a similar manner as inExample 1. The results of measurements of various properties of thatpolyurethane are presented in Table 2.

Example 9

In hexamethylene carbonate diol having a number average molecular weightof 2,000 (1,000 parts), 1,3-propanediol (113 parts) and MDI (515 parts)were evenly mixed with stirring, and the resulting mixture was pouredinto a tray, followed by a reaction at 100° C. Subsequently, apelletized polyurethane (U11) was obtained in a similar manner as inExample 1. The results of measurements of various properties of thatpolyurethane are presented in Table 2.

Example 10

In an ester-modified polysiloxane diol having a number average molecularweight of 5,200 and a siloxane content of 60% (1,000 parts) and PTMGhaving a number average molecular weight of 1,700 (450 parts),1,3-propanediol (190 parts) and MDI (827 parts) were evenly mixed withstirring, and the resulting mixture was poured into a tray, followed bya reaction at 100° C. Subsequently, a pelletized polyurethane (U12) wasobtained in a similar manner as in Example 1. The results ofmeasurements of various properties of that polyurethane are presented inTable 2. The ester-modified polysiloxane diol had been obtainedbeforehand by copolymerizing an alcohol-modified siloxane oil(“KF-6002”, product of Shin-Etsu Chemical Co., Ltd.), which had a numberaverage molecular weight of 3,200 and the below-described structure,with ε-caprolactone.

(n: a number required to give an OH value of 35) TABLE 2 Impact ImpactFlow Melt resilience (%) resilience Hardness M100 TB EB beginningviscosity (1) (2) ratio PU (JIS A) (MPa) (MPa) (%) temp. (° C.) (dPa ·s: 210° C.) 0° C. 23° C. ((1)/(2)) Ex. 6 U8 90 7.9 40.2 407 191 1.9 ×10⁴ 42.4 60.2 0.70 Ex. 7 U9 89 7.8 38.8 375 183 2.2 × 10⁴ 52.7 72.8 0.72Ex. 8 U10 88 7.2 41.0 402 186 1.7 × 10⁴ 44.3 62.5 0.71 Ex. 9 U11 92 8.239.1 386 194 2.9 × 10⁴ 41.0 59.4 0.69 Ex. 10 U12 86 7.1 18.7 352 203 6.1× 10⁴ 62.7 76.6 0.82(Note)PU, M100, TB and EB have the same meanings as indicated in Table 1

From the results of Table 2, the polyurethanes (U8 to U12) of Examples 6to 10, which contained segments B of 1,3-propanediol within the range offrom 1 to 30%, had impact resiliences at 23° C. of from 50 to 90%, andmoreover, their impact resiliences at 0° C. were as high as 0.60 timesor more of their impact resiliences at 23° C. It is, therefore,understood that they had high impact resiliences not affected by changesin outdoor temperature and are suited as cover materials for golf balls.

INDUSTRIAL APPLICABILITY

According to the above-described present invention, a polyurethanehaving high impact resilience can be provided. Its impact resilience isnot affected by outdoor temperature, in other words, its impactresilience does not vary much depending on changes in outdoortemperature. The polyurethane can be used for various applications, andis useful especially as a cover material for golf balls.

1-11. (canceled)
 12. A thermoplastic polyurethane comprising a segment Aformed of a high molecular weight diol, a segment B formed of a lowmolecular weight diol, and a segment C formed of a polyisocyanate, saidsegments A, B and C are bonded together in a linear form by urethanebonds, said high molecular weight diol is at least one diol having anumber average molecular weight of from 600 to 4,000 and selected fromthe group consisting of polytetramethylene ether glycol, polybutyleneadipate diol, polycarbonate diols, polysiloxane diols, and mixturesthereof, wherein said high molecular weight diol, said low molecularweight diol and said polyisocyanate are used in proportions of 100 partsby weight, from 10 to 120 parts by weight and from 20 to 170 parts byweight, respectively, and said thermoplastic polyurethane has an impactresilience at 23° C. of from 50 to 90% and has an impact resilience at0° C. of at least 0.6 times of its impact resilience at 23° C.
 13. Athermoplastic polyurethane according to claim 1, wherein said highmolecular weight diol is polytetramethylene ether glycol having a numberaverage molecular weight of from 1,000 to 2,000, and said high molecularweight diol, said low molecular weight diol and said polyisocyanate areused in proportions of 100 parts by weight, from 11 to 42 parts byweight and from 39 to 76 parts by weight, respectively.
 14. Athermoplastic polyurethane according to claim 1, wherein said highmolecular weight diol is polytetramethylene ether glycol having a numberaverage molecular weight of from 800 to 1,200, and said high molecularweight diol, said low molecular weight diol and said polyisocyanate areused in proportions of 100 parts by weight, from 20 to 30 parts byweight and from 50 to 60 parts by weight, respectively.
 15. Athermoplastic polyurethane according to claim 1 wherein said lowmolecular weight diol is selected from the group consisting of1,4-bis(hydroxyethoxy)benzene, 1,3-propanediol and mixtures thereof. 16.A thermoplastic polyurethane according to claim 1 wherein saidpolyisocyanate is 4,4′-diphenylmethane diisocyanate.
 17. A golf ballcomprising a thermoplastic polyurethane according to claim 1.